Radioactivity detecting apparatus



Apnl 6, 1954 F. s. PHILLIPS 2,674,699

RADIOACTIVITY DETECTING APPARATUS Filed Feb. 11, 1950 L.P.'FILTER H.P. FILTER 65 62 63 l 1 I Y I I. AMPLIFIER RECORDER I 1 37 L .l

F'IGJ.

SITIVITY ER MINUTE) (COUNTS 0 I60 sbo 8 50 9 00 5550 I600 1650717)?) ANODE POTENTIAL F'IG.2.

INVENTOR. FLOYD S. PHILLIPS HIS ATTORNEYS.

Patented Apr. 6, 1954 UNITED STATES ATENT OFFICE RADIOACTIVITY DETECTING APPARATUS Application February 11, 1950, Serial No. 143,629

10 Claims.

The present invention relates to devices for detecting radioactivity and more specifically to new and improved radioactivity detecting apparatus in which one or more of a plurality of radioactivity detectors may be made operable to detect radioactivity in a novel and highly effective manner.

More specifically, the invention has to do with new and improved radioactivity detecting apparatus of the above character which is of special utility in relatively inaccessible places such as bore holes drilled into the earth, for example, although it is not limited to such uses.

It has been proposed, heretofore, to log the radioactivity of earth formations surrounding a bore hole by lowering relatively short and relatively 1on radiation detectors simultaneously in a common housing into the bore hole and recording at the surface the response of one or both of the detectors. The shorter detector has the greater resolving power so that it provides a relatively detailed log of radioactivity which shows relatively thin strata. Its sensitivity is low, however, so that the apparatus must be moved through the bore hole at a relatively low velocity while the log is being made. Where a detailed log is not necessary, the output from the longer detector, or from both detectors is logged. Since the longer detector is more sensitive, the apparatus can be moved through the bore hole at a relatively high velocity during this logging operation. Thus, the apparatus is capable of producing a correlation log at a relatively great velocity, yet enables a detailed log of thin formations to be obtained when desired.

For maximum detector size, as required for maximum sensivity, within a housing small enough to pass readily through a bore hole, the detectors must be snugly fitted one above another in the housing. The conductors required for connecting the detector to apparatus on the other side of the other detector in the housing, therefore, cannot readily be placed between said other detector and the housing. Accordingly, said other detector must be provided with a tube or conduit extending through its active length through which conductors may pass to the other detector. It is, therefore, very expensive and difiicult to manufacture, and, even when manufactured with great care, it is apt to become unstable in operation.

It is an object of the invention, accordingly, to provide new and improved radioactivity detecting apparatus in which one or more of a plurality of radiation detectors may be made operable to detect radiation, as desired, in a novel and highly effective manner.

Another object of the invention is to provide new and improved radioactivity detecting apparatus of the above character in which radioactivity may be detected selectively with detectors of difierent sensitivities.

A further object of the invention is to provide new and improved radioactivity detecting apparatus of the above character which is capable of use in relatively inaccessible places such as bore holes drilled into the earth, for example, and which may be controlled in a simple and eiiecti've manner from a remote location such as the surface of the earth, for example.

Still another object of the invention is to provide new and improved radioactivity detecting apparatus of the above character in which a single control circuit may be employed to control the operation or a plurality of radiation detectors.

These and other objects of the invention are attained by providing radioactivity detecting apparatus comprising a plurality of radiation detectors each having cathode means and anode means mounted in an evacuated envelope. The several detectors are suitably designed so that the respective anode potentials at which they become operative as radiation detectors are different and the anode means of the detectors are connected in series to an adjustable source of anode potential. With this construction, one or more detectors may be rendered operative selectively to detect radiation by proper adjustment of the anode potential provided by the source.

In a. preferred embodiment designed for use in inaccessible places such as bore holes drilled into the earth, for example, the detectors may be mounted in longitudinally spaced apart relation in a housing adapted to be lowered into a bore hole. The anode means of the detectors are connected in series and means may be pro- Vided for controlling from a relatively remote point such as the surface of the earth, for example, the potential applied to the anode means circuit, thereby to render one or more of the detectors effective to detect radiation as desired.

Additional objects and advantages of the invention will be apparent from the following detailed description of a representative embodiment, taken in conjunction with the accompanying drawings in which:

Fig. 1 illustrates schematically typical radioactivity detecting apparatus constructed accordactivity detecting apparatus I9 is adapted to be raised and lowered through a bore hole H by means of a supporting cable -l2*and-'winch (not.

shown), as is well known in thea-rt. The bore hole I! generally contains a conducting fluid. l3 1 such as drilling mud, for example, and may also. have a metallic casing (not shown) inserted therein.

The detecting apparatus Iii may comprisea waterproof pressure-resistant housing l4, preferably made .of suitableconducting material so as to provide an electrical ground return from the electronic equipment contained therein through the bore hole fluid l3 and surrounding earth formations to the surface equipment. additional conductor can be provided in the cable I2 to serve as a ground return, if desired, in which case the. housing, It may be made of any suitable material- Mounted one above the other in the housing 14 and snugly fitted therein are a pair of radiation detectors IS'and "iSwhich" may be of the type known in the art as Geiger-Mueller counters. The detector lfiunay comprise, for example, a central anode is and a coaxial cathode of substantially cylindrical shape disposed in an evacuated envelope containing gas at a suitable pressure. According to the usual practice, the detector i6 is made relatively short so as to enable it to provide a relatively finely detailed log of radioactivity whichwill'show relatively thin formations. Because of its short length, however, its sensitivity is relatively low so that the housmg 2'4 -should be moved'through the bore hole at a lower velocity when a log is being made.

The detector l5 likewise may comprise a central anode P and a coaxial cathode l8 'of substantially cylindrical shape disposed in an evacuated envelope containing gas at a suitable pressure. The detector E5," on the other hand, is made relatively long so that it will'have suffic'ient sensi-' tivity to enable a relatively less finely detailed log of the radioactivity of the formations surround-' ing the bore hole H to be obtained While the housing id is moved through the bore hole at a relatively high rate of speed.

According to the invention, the anode [9 of the detector it is connected in series with the anode l1 otthe detector l5 by aconductor 2| and the detectors l5 and K6 are designed to have different starting potentials so thateither one or both may be rendered effective to detect radioactivity by controlling the magnitudeof the potential applied tothe anode :l of the detector 15. Control of the anode potential may be effected in any desired manner, as, for example, by grounding the cathodes. i8 and. Not the detectors l5 and IE5, respectively, to the housing i l by the conductors 22 and 23, respectively, and connecting the anode ll of the detector l5 selectively to different taps on a suitable source of high potential D. C.

Thismay be accomplished by connecting the anode I7 through a conductor 24 and a suitable inductance 25 to the movable contact 26 ofa re-v lay 21, which is adapted to be moved selectively Of course, an

into engagement with either of two fixed contacts 28 and 29. The inductance 25 serves to keep the output pulses from the detectors l5 and 13 out of the D. C. supply. The fixed contacts 28 and 253 are connected to suitable taps 30 and 3|, respectively, on a resistance 32, one end of which is grounded to the housing It at 33 and the other end of which is connected by a conductor 35 to the positive terminal of a conventional high potential D. C. power supply 35, preferably having a well regulated output.

lhe DC; power. supply 35 may be energized by volt, 60 cycle A. 0., for example, supplied by a suitable source 35 preferably located at the surface of the earth. One terminal of the source 36 may be grounded at 3? and its other terminal may be-connected by a conductor 38 to an insulated conductor 39 in the supporting cable [2. The lower end of the conductor 39 is connected to the primary winding 58 of a transformer ll mounted in the housing 24, the other terminal of which is grounded to the housing Hi at :2 through a condenser shunt with the winding of the relay and it'provides a low impedance path for A. C. oi the supply frequency. One terminal of the secondary winding as of the transformer ll is grounded to the housing at 45 and the other terminal is connected to one terminal of the D. C. power supply 35, the circuit being completed through a conductor 46 which is grounded to the casing M at M.

Operation of the stepping relay 2'! may be effected in any desired manner as, for example, by means of a switch 48 at'the surface of the earth. The switch 43 has a movable contact 29 which may be moved selectively into engagement with either of two fixed contacts 50 and 5|. The contact 50 is connected to one terminal of the A. C. source 35 while the contact Si is connected to one terminal of a suitable source of D. C. 52, the other terminal of which'is grounded at 53. With this construction, each time the switch contact 49 is moved into engagement with the contact 5|, the relay 2'! is-energized and moves its contact 28 out of engagement with one of the contacts 28 or 29 and into engagement with the other. The next time D. C. is applied to the relay 21' by operation of the switch 48, the movable contact 26 'on the relay 2? returns to its initial position.

The pulse output from the detectors l5 and 16 may be fed from the anode H of the detector l5 through a D.'C.'blocking condenser 5d and a conductor 55 to one terminal of a conventional pulse amplifier 56, another terminal of which is grounded to the housingv i l by a conductor 5'1. The amplifier 56 also receives D. C. power from the power supply 35 through a conductor 58 connected to a tap 58 on the resistor 32.

The output of the amplifier 58 is fed through a conductor 59, the conductor 33 in the supporting cable l2, a conductor 60 and a D. C. blocking condenser 6| to a second amplifier 62, the output of which maybe Supplied to a conventional recorder 63 which preferably records the outputs of the detectors l5 and I6 as a function of depth in the bore hole.

Preferably, a conventional low pass filter 64 should be interposed between the conductor 38 and the switch 48 for the purpose of keeping the relatively high frequency pulse output from the detectors l5 and [6 out of the electrical energy sources 36 and 52.. Similarly, aconventional high. pass .filter .65 shouldpreferably be interposed: be-.. tween the conductor 60 and the amplifier 62 for The condenser it is connected in 5 the purpose of keeping low frequency A. C. from the source 36 and D. C. from the source 52 out of the recording system.

Th operation of the detecting apparatus will be more easily understood from the detector characteristic curves shown in Fig. 2. The solid curve 66 in Fig. 2 is a typical plot of the sensitivity of the detector I6 as a function of the potential applied to the anode I9 thereof, sensitivity being measured in units of counts per minute." The dashed curve 61 is a plot of a typical sensitivity characteristic for the detector I5. It will be noted that the detector I6 is designed to have a lower starting potential than the detector I 5 and, since the detector I6 is shorter, it is not as sensitive. However, being shorter, it is better able to give indications of relatively thin formations.

In order to produce a log of the output of the shorter detector I6, the switch 48 is manipulated to energize the relay 21, thereby moving its movable contact 26 out of engagement with the fixed contact 28 and into engagement with the lower potential contact 29. If the detectors I5 and I6 have characteristics as represented by the curves 6'! and 66, respectively, in Fig. 2, the position of the tap 3| should be so chosen that approximately 910 volts will be applied to the anodes I! and I9 of the detectors I5 and I 6, respectively, when the switch contact 26 is in this position. This corresponds to the point 58 on the curve 66. Upon inspection of the curves 66 and 61 in Figs. 2, it will be apparent that, under these conditions, the detector IE will be operative to detect radioactivity but the detector I5 will be inoperative. Therefore, if the housing I4 is moved relatively slowly through the bore hole II, the recorder 63 will provide a radioactivity log which will distlinlguish thin formations traversed by the bore e I I.

In order to obtain a less finely detailed log at a higher rate of speed, the switch 48 is again manipulated to move the movable stepping switch contact 26 out of engagement with the fixed contact 29 and into engagement with the contact 28 thereby applying a higher potential, say 970 volts, to the anodes I! and I9 01 the detectors I5 and I6, respectively. This corresponds to the points 69 and on the curves B6 and 61, respectively, in Fig. 2. As can be seen from Fig. 2, under these conditions both detectors will be operative to detect radioactivity and the sensitivity of the system is greatly increased. Therefore, the logging apparatus may be run through the bore hole II at a substantially greater speed than when only the single short detector I6 is in use.

The desired difference in the starting potentials of the detectors I5 and I6 may be obtained in any known manner as by varying the pressure or the composition of the gas in each of the detectors as desired, for example. For more detailed information about detectors constructed so as to have different starting potentials, reference is made to an article entitled The Factors Influencing the Plateau Characteristics of Self- Quenchin Geiger-Mueller Counters by W. D. B. Spatz, Physical Review, Volume 64, Numbers 7 and 8, October 1 and 15, 1943, pp. 236-240 inelusive.

The invention, therefore, provides a novel and a highly effective apparatus for detecting radioactivity. By designing the detectors so as to have different starting potentials and connecting their anodes in series, one or more of them may be brought into operation selectively, as desired, by proper adjustment of the anode voltage. This is highly advantageous in applications where the detecting apparatus is to be used in inaccessible places since it enables a plurality of detectors to be controlled without the necessity for running conductors or the like through any of the detectors.

It will be understood that the specific embodiment disclosed herein is susceptible of numerous modifications in form and detail within the scope of the invention. For example, other means than that shown may be employed for applying an adjustable direct current voltage to the anodes of the detector tubes, as will be apparent to those skilled in the art. Further, multiple-element detectors of the type shown in Patents Nos. 2,397,071 and 2,489,133, for example, may be employed instead of the simple illustrative forms of detectors described above. Also, the invention is not restricted to apparatus including only two detector tubes but may be applied with equal effectiveness to an apparatus comprising a plurality of tubes, one or more of which are to be rendered eifective selectively to detect radioactivity. The specific embodiment described and shown in the accompanying drawing, therefore, is not to be regarded as limiting the scope of the appended claims.

I claim:

1. In radioactivity detecting apparatus, the combination of a plurality of radiation detectors, each having electrode means including anode means and cathode means and having different starting potentials, an energizing circuit having one terminal connected to the anode means of said detectors and another terminal connected to the cathode means of said detectors, a D. C. source interposed in said circuit and means facilitating adjustment of the amplitude of the potential of said source to values corresponding to said different starting potentials to render said detectors selectively operable.

2. In radioactivity detecting apparatus, the combination of a plurality of radiation detectors of different resolving powers, each having electrode means including anode means and cathode mean and haviing difierent starting potentials, an energizing circuit having one terminal connected to the anode means of said detector and another terminal connected to the cathode means of said detectors, a D. C. source interposed in said circuit and means facilitating adjustment of the amplitude of the potential of said source to values corresponding to said diiierent starting potentials to render said dectectors selecti ely operable.

3. In apparatus for detecting radioactivity in relatively inaccessible locations, the combination of at least two radiation detectors adapted to be positioned in an inaccessible location, said detectors having different starting potentials and each having anode means and cathode means, an energizing circuit including the anode means of said detectors and an adjustabl amplitude D. C. source in series, means for controlling the amplitude of the potential output of said D. C. source from a relatively remote observation position to provide potential outputs corresponding to said respective starting potentials to render one or both of said detectors operable to detect, and mean at said observation position for exhibiting a function of the output of one or both of said detectors.

4. In apparatus for detecting radioactivity in a b r -hol -v .drillcdinto theeartl at e; c m er: tion-of a housing adaptedtQbe-m yed through detect, radioactivity, and means at the surface of the earth for exhibiting a function-of the output of one or both of said detectors 5. In apparatus for detecting radioactivity in a bore hole drilled into the earth, the combination of a housing adapted to be moved through a bore hole, at least two longitudinally spaced apart radiation detectors in said housing, said detectors having different starting potentials and each having anode means and cathode means, an energizing circuit including the anode means of said detectors and a D. C. source in series in said housing, electrical means in the housing for adjusting the amplitude of the output of said D. C. source to provide potential outputs coresponding to said respective starting potentials to render one or both of said detectors selectively operable to detect radioactivity, electrical circuit means connected to said electrical adjusting means and extending tothe surface of the earth, and control means connected to said circuit means at the surface of the earth for controlling said adj usting means.

6. In apparatus for detecting radioactivity in a bore hole drilled into the earth, the combination of a housing adapted to be moved through a bore hole, at least two longitudinally spaced apart radiation detectors in said housing, said detectors having different starting potentials and each having anode means and cathode means, a source of D. C. in said housing, adjustable voltage divider means connected to said D. C. source, an energizing circuit including the anode means of said detectors and said voltage divider means in series, relay means in said housing for actuating said voltage divider means, circuit means including at least one conductor extending from said relay means to the surface of the earth, and control means interposed in said circuit means at the surface of the earth for controlling the operation of said relay means.

'7. In apparatus for detecting radioactivity in a bore hole drilled into the earth, the combination of a housing adapted to be moved through a bore hole, at least two longitudinally spaced apart radiation detectors in said housing, said detectors having different starting potentials and each having anode means and cathode means, an A. C. energized source of D. C. in said housing, adjustable voltage divider means connected to said D. C. source, an energizing circuit including the anode means of said detectors and the voltage divider means in series, relay means for actuating said voltage divider means, circuit means including at least one conductor connected to the A. C. input side of said D. C. source and to said relay means, A. C. and D. C. sources disposed at heiz riace piithei rthi andt w ch newmcans for .conne tineseid and DHC sourc 581E612 tively in said circuit means.

8. In apparatus; forv detecting, radioactivity ,in

. a bore drilled into the-.earth the:combination;

of a housing adaptedto, be moved through @a bore hole, atJeast two longitudinally spaced apart radiationudetectors in said housing, said detectors having different starting potentials and each hayinganode meansand cathodev means, an A. C. energized source of D. C. in; said housing adjustable:yoltage divider means connected to said,

D.,C. source,- ,an energizing circuit including the anode rmeans of. said-detectors and. the voltage divider means in series, relay means for actuating said voltage divider-means; circuit means including at least one conductorhconnccted ,to the;

A. C. input side of said D. C. source and tosaid relay means, means connected in shunt. with said relay means and forming a low'impedance path,

to A.-C., A. C. and D.,C. sources disposed atv the surface of the earth, switching means for con-, necting said-A. C. and D. C. sources selectively in said circuit means, amplifier means in the housing. having input terminals connected to said detector anode means and cathodemeans, respectively,.and. having output terminals connected in said circuit means, first filter means for keeping periodically .varying signals .out of said voltage,

divider means and forkeeping D. C. out, of the input circuit of said amplifier means,.recording means located at the surface of the earth, second amplifier means having. input-terminals ,connected to said circuit means. at the surface of the earth andhaving output terminals connected to said recording means, low pass. filter means interposed between said circuit means. and said switching means at. the surface of the earth, and high pass filter means interposed between said circuit means and said second amplifier means.

9.,In radioactivity detecting apparatus, the combination of a plurality of radiation detectors havingstarting potentials in inverse relationship to their resolvingpowers, a sourceof adjustable direct, potential, and an energizing circuit for applying the direct potential to all said. detectors in parallel, whereby said detectors arerendered cumulatively operable with increasing applied potential, starting with the detector having the highest resolving, power.

10, In radioactivity, detecting apparatus, the combinationv of a plurality of radiation detectors having different resolving powers and ,different starting potentials, the lowest starting potential being associated with the detector having thehighest resolvingpower, means for applying a direct potential simultaneously ,to.-all said detectors, andmeansfor adjusting saidpotential whereby detectors of progressively lower resolvingpower are rendered successively operable with increasing applied potential.

Referenccs Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,378,408 Herzog June 19, 1945 2,3 1,0 3 Howell Dec, 18, 1945 2,4 4, 81 Howell June 28, 1949 2,481,014 Herzog Sept.- 6, 1949 2,508,772 Pontecorvo May 23,1950 

